May 10, 2013 

Gregory Nudd 

Tilcson Electric Power CDmpang 

88 East Broaqway Blvd (85701) 

Mail Stop HQW602, Post Office Box 711 

Tucson, Arizona 85702 

Submitted via email 

United States Environmental Protection Agency 

Region 9, Air Division (AIR-2) 

75 Hawthorne Street 

San Francisco, CA 94105 

Telephone (520) 918-8351 

Email: EBakken@tep.com 

RE: Visibility Modeling and Control Cost Information Relating to H Wilson Sundt 

Generating Station, Tucson, Arizona 

To Mr. Nudd: 

Tucson Electric Power Company (TEP), a wholly-owned subsidiary of UniSource 

Energy Corporation (NYSE: UNS), owns and operates the H. Wilson Sundt Generating 

Station (Sundt) in Tucson, Arizona. The Sundt station consists of four electricity 

generating units, three of which are fired by natural gas and one (Unit 4), which is 

predominantly coal-fired, but is also capable of firing natural gas. 

On December 22, 2012, EPA issued a proposed rule disapproving certain aspects of 

Arizona's State Implementation Plan (SIP) for Regional Haze. One of the provisions that 

EPA proposes to disapprove is the Arizona Department of Environmental Quality's 

(ADEQ) conclusion that Sundt Unit 4 is not "BART-eligible" because the unit was 

"reconstructed" after August 7, 1 977, and was therefore, not "in existence" as of that 

date, which is one the requirements for BART eligibility. 

TEP submitted comments dated March 6, 2013, regarding EPA's proposal, in which we 

provided a detailed analysis supporting ADEQ's conclusion that Sundt Unit 4 is not 

BART-eligible. Those comments are attached (Attachment A). On March 29, 2013, 

ADEQ proposed revisions to its Regional Haze SIP, reaffirming its conclusion that Sundt 

Unit 4 is not BART-eligible. TEP strongly supports ADEQ's position both on technical 

grounds, as well as Arizona's legal argument that its actions relating to the Arizona SIP 

are within the authority granted under the Clean Air Act and are in compliance with the 

Act's provisions. 

That said, TEP was notified via email on February 27, 2013, that EPA was proceeding 

with a BART determination for Sundt Unit 4, and that EPA welcomed any information 

TEP could provide relevant to such an analysis. Separately, EPA provided a draft report 
Mr. Gregory Nudd 

May 10, 2013 

Page 2 

and supporting documents prepared on behalf of EPA documenting a Five-Factor Best 

Available Retrofit Technology (BART) analysis1 on Sundt Unit 4 ("draft BART report"). 

Notwithstanding TEP's position that Sundt Unit 4 is not BART eligible, TEP provides 

the following comments on the draft BART report, and additional information to assist 

EPA in developing a thorough and accurate analysis, should they elect to propose and 

ultimately finalize a BART determination for Sundt Unit 4. 

TEP will continue to evaluate the data and analysis that EPA has provided and will 

respond with any new information as available. Similarly, TEP would welcome any new 

or updated analysis that EPA may develop. 

Sundt Unit 4 Design and Operational Information 

Sundt Unit 4, completed in 1967, was the final of four steam electric generating units 

constructed as part of the Irvington Generating Station. The Irvington Generating Station 

was subsequently renamed the H. Wilson Sundt Generating Station, and is referred to as 

"Sundt". Sundt Unit 4 was originally constructed to fire oil or natural gas. In the 1980s, 

Sundt Unit 4 was converted to bum coal in response to a prohibition order issued under 

Section 301 (c) of the Power Plant and Industrial Fuel Act of 1978. As part of the coal 

conversion, the unit was equipped with a fabric filter for particulate control. In 1999, the 

unit was upgraded with low-NOx burners and overfire air, designed to meet Phase II 

Acid Rain requirements. 

The coal conversion did not affect the unit's ability to bum natural gas, however, the 

generating capacity of the unit while firing coal was reduced compared to its capacity on 

natural gas. That is primarily due to fact that the amount of coal that can be introduced to 

the boiler is limited by the size of the boiler. Excess coal injection causes the flame to 

impinge on the back wall of the boiler which damages the boiler tubes. 

TEP reports the capacity of Unit 4 to the Energy Information Association (EIA) as 173 

MW as that is the nameplate capacity of the unit while firing natural gas. However, the 

maximum gross capacity that the unit could operate at, for a sustained period of time, 

while burning coal is approximately 130 MW. This maximum capacity on coal is evident 

on the chart in Attachment B, which shows the actual gross load of Sundt Unit 4 for all of 

calendar year 2011, a year during which the unit was predominantly coal-fired. 

While Sundt Unit 4 is capable of firing natural gas, it has operated predominantly as a 

coal-fired unit since the coal conversion. However, recently Unit 4 has been operating on 

natural gas for extended periods of time due to historically low natural gas prices. In fact, 

Sundt Unit 4 operated in natural gas-fired mode for significant portions of 2009, 2010, 

and 2012. Again, in 2011, Unit 4 primarily burned coal. 

The draft BART report prepared for EPA used a mix of operating and emissions data 

from 2008 through 2011. TEP believes that EPA's analysis should be based on operating 

and emissions data for 2011, as that is the most current year that the unit operated 

1 UNCI ICF- Technical Analysis of Arizona and Hawaii Regional Haze FIPs: Task 7: Five-Factor BART 

Analysis for TEP Sundt (Irvington), delivered October 9, 2012 
Mr. Gregory Nudd 

May 10,2013 

Page 3 

primarily on coal and its operation during that year is the most representative for BART 

analysis purposes. The table below presents the appropriate data for use in a BART 

analysis on Sundt Unit 4. 

Generation 555,491 MWh 

Gross Capacity 130 MW 

Capacity Factor 49% 

Average S02 Emission Rate 0.729 lbs/MMBtu 

Average NOx Emission Rate 0.445 lbs/MMBtu 

Cost Estimates for Control of 802 and NOx 

TEP reviewed the draft BART report, including the accompanying spreadsheets detailing 

the cost estimates for the control options evaluated as potential BART. Based on TEP's 

review and our understanding of Sundt Unit 4, it did not appear that the cost estimates 

considered site specific factors that could play a significant role in the total cost of 

retrofitting Sundt Unit 4 with air pollution controls. Therefore, TEP hired Burns and 

McDonnell (BMcD) to review the draft BART report and to prepare comparative cost 

estimates for the control options under consideration. 

BMcD is a world leader in air pollution control projects and has provided engineering 

design and construction management on hundreds of air pollution control projects over 

the past 40 years. In addition, BMcD has been providing engineering services to TEP at 

Sundt for several years, and as a result they are very familiar with the design and 

operation of that facility. 

BMcD's cost estimates were, for each control option, greater than the cost estimates 

prepared by EPA's contractor (see Attachment C). Three of the five three technologies 

evaluated significantly exceeded the EPA's screening cost effectiveness threshold of 

$5,000/ton (see Table 1, Attachment C). 

Selective Catalytic Reduction (SCR) 

Dry Flue Gas Desulphurization (DFGD) 

Wet Flue Gas Desulphurization (DFGD) 

$7,874/ton 

$9,359/ton 

$8,229/ton 

The differences between the estimates prepared by BMcD and those in the draft BART 

report are detailed in the BMcD report. In general terms, the reasons that the estimates in 

the draft BART report are lower than those prepared by BMcD can be grouped as 

follows: 

• Failure to take into account site-specific features of Sundt Unit 4 such as: 

o congestion in the areas where new equipment would be installed or tied-in 

due to the presence of boiler steel, supporting structures, coal handling 

equipment and the existing baghouse, 

o the horizontal duct arrangement of the existing air preheater, which would 

require extensive reconfiguring and/or replacement of the air preheater for 

installation of SCR, 
Mr. Gregory Nudd 

May 10,2013 

Page4 

o the presence of the Sundt Unit 3 cooling water recirculation line routed 

adjacent to Unit 4, where new equipment would normally be located, 

• Failure to adjust technology unit costs to account for the fact that Sundt Unit 4 is 

relatively small and unit costs increase with decreasing facility size, 

• Failure to escalate previously developed cost estimate figures to the current date, 

• Underestimation of owners costs and costs associated with engineering and 

construction management 

• Underestimation of operation and maintenance costs for complex systems. 

The BART Guidelines2 provide for incorporation of site-specific factors, or 

"elements ... that are not addressed by the Cost Control Manual", in determining the cost 

of control for BART. Some of these elements cannot be identified through literature 

research, and require knowledge of, or at a minimum a visit to the site. The most 

significant site-specific factors relevant to determining BART for Sundt Unit 4 have been 

identified by BMcD, and these factors should be incorporated into any BART 

determination for that facility. 

Visibility Modeling 

The draft BART report includes the results of visibility modeling for existing conditions 

(i.e. Base Case) and 11 control retrofit scenarios. TEP hired AECOM to (1) review the 

results of modeling analysis included in the draft BART report, (2) make 

recommendations for appropriate modifications to the modeling approach used in the 

draft BART report, and (3) to conduct visibility modeling on select control scenarios 

incorporating any such modification (see Attachment D). 

Modeling Apoach 

The modeling approach used by AECOM was generally in accordance with that used to 

develop the draft BART report, with two important modifications described below. 

While AECOM conducted its modeling using CALPUFF version 5.8, they point out in 

their report that that version of CALPUFF suffers from coding "bugs" and uses outdated 

chemistry algorithms. In fact, there have been several studies conducted over the last few 

years demonstrating that the chemistry and the dispersion functions of CALPUFF version 

5.8 over-estimate the visibility impacts of NOx emissions in Class I areas and thus, 

erroneously over-estimate the visibility improvements from proposed BART controls 

leading to biased cost benefit ($/dv) values. TEP believes that EPA should adopt a newer 

version of CALPUFF (version 6.42) as the approved regulatory version for Regional 

Haze modeling. 

AECOM also identified background amonia as an area to improve the modeling 

approach. Ammonia plays an important role in the formation of compounds, such as 

amonium nitrate, that potentially could contribute to visibility impairment at certain 

2 Regional Haze Regulations and Guidelines for BEST Available Retrofit Technology (BART 

Detenninations, Fed. Reg. vol. 70, page 39127 
Mr. Gregory Nudd 

May 10,2013 

Page 5 

Class I areas. Therefore, the background ammonia concentration used in visibility 

modeling is critical because amonia is a precursor to particulate ammonium nitrate. 

The draft BART report used a default value of 1 ppb for ammonia background 

concentration for all months of the year. This value tends to overestimate the visibility 

benefits associated with reductions of NOx, particularly in the winter months. Therefore, 

in their analysis, AECOM used amonia background concentrations that were taken 

from actual data from the IMPROVE monitoring network. In the prepublication version 

of the EPA proposed rule to approve additional portions of Arizona's SIP for Regional 

Haze, received by EPA on May 9, 2013, EPA acknowledges the value of considering 

monitored IMPROVE data "in support of ... RH planning efforts"(p. 23). Likewise, EPA 

should recognize the value of monitored data in visibility modeling for BART. 

Recently, the IMPROVE monitoring network began to incorporate routine measurements 

of gaseous amonia at specific sites. Data from the IMPROVE network includes 

monthly amonia measurements at several sites, including one in southern Arizona 

(Chiricahua). A review of the measurements taken to date at this site (see Fig. 4-1, 

Attachment D) indicates that amonia concentrations below 1 ppb (e.g., 0.5 ppb) are 

present at this site in winter. Use of those values will more accurately predict the 

visibility improvements expected from the addition of BART controls for NOx. 

Stack Parameters 

The draft BART report identified the data source for stack parameters as being the 

National Emission Inventory 2008, Version 2. To assist in determining if the reported 

values for stack temperature and stack velocity were appropriate for use in modeling, 

TEP developed a chart for each of these parameters by plotting actual measured stack 

temperature and velocity versus gross load. Using these charts, TEP determined that the 

value for stack velocity used in the draft BART report (79 fils), corresponded to operation 

of Sundt Unit 4 at approximately 60% of full load (see Attachment E). The value for 

stack temperature used in the draft BART report corresponded to operation at full load. 

Since the emission rate used in the modeling corresponds to the maximum daily average 

hourly emissions over a period of three consecutive years, excluding periods of start-up, 

shutdQwn and malfunction, it is reasonable to assume that those emissions would 

correspond to full load operation. Therefore, TEP provided AECOM with stack a 

velocity value associated with full load operation to use in their modeling. 

Predicted Visibility Improvement 

AECOM modeled potential visibility improvement for two different candidate BART 

control options that were identified in the draft BART report: 

1. Dry Sorbent Injection (DSI) I Selective Non-Catalytic Reduction (SNCR) 

2. Dry Flue Gas Desulphurization I Selective Catalytic Reduction 

For these scenarios, AECOM modeled visibility impairment relative to natural conditions 

at the Class I areas within 300km of Sundt Unit 4 and found that only Saguaro National 
Mr. Gregory Nudd 

May 10,2013 

Page 6 

Park (East and West) had visibility impairment in excess of the 0.5 delta-dv (see table 

5.1, Attachment D) "contribution" limit established by EPA. Therefore the AECOM 

analysis concentrated solely on this Class I area and more specifically on Saguaro 

National Park East. 

The AECOM report shows the largest visibility benefits at the Saguaro National Park 

East for the DSIISNCR and DFGD/SCR controls to be 0.164 and 0.128 delta-dv, 

respectively. It is worth noting that the less stringent emission control option resulted in 

greater visibility improvement. 

Using the BMcD estimates for annualized costs, the visibility cost effectiveness for these 

two control scenarios are: 

DSIISNCR 

DFGD/SCR 

$38,000,000/dv 

$212,000,000/dv 

Each of these control scenarios are considerably more than the benchmark of $20 million 

per deciview that the Federal Land Managers previously established a as a threshold 

above which the degree of visibility improvements is not justified relative to its cost. 

Conclusion 

TEP remains steadfast in it assertion that Sundt Unit 4 is not BART-eligible. However, 

EPA appears to be moving forward with a five-factor BART analysis for Unit 4, as 

evidenced by a draft BART report provided to TEP by EPA. TEP hired industry experts 

to review the draft BART report, to develop cost estimates for the control options for S02 

and NOx, and to conduct visibility modeling for specific control scenarios. 

Based on the cost estimates, TEP concludes that three of the five technologies evaluated 

(SCR, DFGD, and WFGD) significantly exceeded the EPA's screening cost effectiveness 

threshold of $5,000/ton, and should therefore, be determined to be not cost effective as 

BART. 

Based on the modeling, TEP concludes that each of the two control scenarios evaluated 

exceeded the Federal Land Managers visibility cost effectiveness of $20,000,000/dv, and 

should therefore, be determined to be not cost effective. 

If you have any questions regarding the information contained in or attached to this letter, 

please feel free to contact me. 

Sincerely, 

4� 

Erik Bakken 

Director, Corporate Environmental Services 

and Land Management 
Mr. Gregory Nudd 

May 10,2013 

Page 7 

Attachments 

A TEP Comments to EPA Proposed Approval/Disapproval of the Regional Haze 

SIP for Arizona, March 6, 2013 

B Sundt Unit 4-2011 Gross Load 

C Bums & McDonnell Report- Tucson Electric Power Sundt Unit 4 BART 

Review, May 9, 2012 

D AECOM- Visibility Improvement Analysis for Candidate BART Control 

Options: Sundt Unit 4, May 2013 

E Sundt Unit 4 - Plot of Stack Velocity versus Gross Load 

Cc: Eric Massey, ADEQ 

Colleen McKaughan, EPA 

Mark Mansfield, TEP 
ATTACHMENT A 
March 6, 2013 

Gregory Nudd 

TUcson Electric PowerCDmpang 

88 East Broadway Blvd (85701) 

Mail Stop HQW602, Post Office Box 711 

Tucson, Arizona 85702 

Submitted via Federal e-Rulemaking Portal 

United States Environmental Protection Agency 

Region 9, Air Division (AIR.-2) 

75 Hawthorne Street 

San Francisco, CA 94105 

Telephone (520) 918-8351 

Email: EBaken@tep.com 

RE: EPA Docket ID No. EPA-R09-0AR-2012-0904 (77 FR 75704; December 21, 2012) 

Dear Mr. Nudd: 

Tucson Electric Power Company (TEP), a wholly-owned subsidiary of UNS Energy 

Corporation (NYSE: UNS), respectfully submits these comments to the Environmental 

Protection Agency (EPA) regarding the Proposed Rule; Partial Approval and 

Disapproval of Air Quality Implementation Plans; Arizona; Regional Haze and Visibility 

Impacts of Transport, Ozone and Fine Particulates ("Proposal"). EPA issued a 

supplemental notice on February 4, 2013, (78 FR 7702) extending the comment period by 

30 days to March 6, 2013. 

TEP owns and operates electric generation, transmission, and distribution assets that 

safely and reliably serve more than 400,000 customers with affordable electricity in 

Southern Arizona. TEP owns and operates fossil-fired electricity generating units in 

Arizona, including the H. Wilson Sundt Generating Station. Actions considered under 

EPA's Proposal could potentially subject Unit 4 at this facility to emission limitations 

under the Regional Haze Rule.1 Therefore, EPA's Proposal is of great importance to TEP. 

Sundt Unit 4 is not BART eligible 

In 2007, while the Arizona Department of Environmental Quality (ADEQ) was 

developing its Regional Haze State Implementation Plan (SIP), TEP provided 

information to ADEQ to assist in determining the BART eligibility of Irvington 

Generating Station Unit 4. The station has since been renamed as the H. Wilson Sundt 

Generating Station and will be referred to hereafter as "Sundt". The information TEP 

provided, documents that Sundt Unit 4 underwent "reconstruction" in the 1980s as part of 

a coal conversion project, and was therefore, not "in existence" on August 7, 1977 (one 

of the requirements for BART eligibility). Using that information, ADEQ concluded that 

1 40 CFR 51.308 - Regional haze program requirements 
EPA-R09-0AR- 201 2-0904 

March 6, 201 3 

Page 2 

Sundt Unit 4 is not a BART eligible unit and, therefore, BART requirements are not 

applicable. On March 2, 2011, ADEQ submitted Arizona's Regional Haze SIP to EPA, 

without BART requirements for Sundt Unit 4. 

On November 22, 2011, TEP received a letter from EPA (dated November 17, 2011) 

stating that EPA was preparing a Regional Haze Federal Implementation Plan (FIP) for 

Arizona, and would "revisit" ADEQ's decision regarding the BART eligibility of Sundt 

Unit 4. 

On March 16, 2012, TEP received a letter from EPA, dated March 14, 2012. This letter 

explained the basis for EPA's position regarding BART eligibility for Sundt Unit 4. 

EPA's justifications for BART eligibility is premised on the fact that Congress intended 

the BART provisions to apply to sources which had been 'grandfathered' from new 

source review permit requirements, and Sundt Unit 4 was exempted from new source 

review at the time of the reconstruction, therefore, the unit is BART eligible. 

On April 18, 2012, Hunton and Williams, on behalf of TEP submitted a letter to EPA in 

response to the March 14 letter, providing a detailed legal framework supporting TEP's 

and ADEQ's position that Sundt Unit 4 is not "BART eligible". That letter is attached 

and hereby incorporated into these comments. 

In the Proposal, EPA accepts TEP's and ADEQ's assertion that the coal conversion 

project qualified as a "reconstruction" under the Regional Haze Rule. However, EPA 

concludes that "the Unit remains BART -eligible because it did not go through NSR/PSD 

permitting" [77 FR 75722]. The Proposal footnotes an internal EPA memorandum [77 

FR 75722 footnote 97] that provides additional detail regarding EPA's view of BART 

eligibility for Sundt Unit 4. In this memorandum, EPA states that the exemption from 

BART for sources reconstructed after August 1977, "is introduced in the BART 

Guidelines" [40 C.F.R. Part 51 App. Y (hereinafter "Appendix Y")], however, EPA 

claims that Appendix Y is "not binding with respect to TEP Sundt Unit 4 because it is not 

part of a fossil fuel-fired electric generating plant with a total generating capacity in 

excess of 750 MW". 

While Appendix Y is not binding on Arizona with respect to Sundt Unit 4, in providing 

the guidance EPA did "encourage States to follow the guidelines for all source 

categories" in order to address "concerns about equitable application of the BART 

requirement to source owners with similar sources in different States" [70 FR 39108]. As 

a federal agency, EPA must apply the Regional Haze Rule consistently across states and 

the guidelines are the means by which EPA itself, intends to ensure that consistency is 

maintained. For EPA to claim it can ignore these guidelines, in its evaluation of a 

particular state's SIP, is arbitrary and capricious. 

Furthermore, EPA's explicit preference for states to apply Appendix Y to all source 

categories is in direct conflict with EPA's conclusion that the State of Arizona was 

incorrect in applying those guidelines, as it did, with respect to BART eligibility of Sundt 

Unit 4. 
EPA-R09-0AR-2012-0904 

March 6, 2013 

Page 3 

Appendix Y expressly provides that any emissions unit for which a reconstruction 

"commenced" after August 7, 1977, is not BART eligibli, and contains no exceptions or 

qualifications to this broad exemption. 

Footnote 9 in the preamble to the BART Guidelines3, referenced in the internal EPA 

memorandum, is not to the contrary, as it merely reflects the reality that post-1977 source 

reconstructions, in general, would have gone through NSRIPSD permitting. That 

footnote does not, nor could it contradict the plain, unqualified language of EPA's rule 

text that exempts "any" post-1977 reconstruction. In the context of the Clean Air Act the 

word "any" has an expansive meaning. 

Likewise, while the preamble statement observing that BART was intended to "apply to 

sources which had been 'grandfathered"' from NSR permitting requirements4 is generally 

true, it does not follow that BART applies either to all "grandfathered" sources (it does 

not apply, for example, to sources that were in operation before 1962) or to sources, like 

Sundt Unit 4, that were not grandfathered but instead were exempt from NSR permitting 

requirements as a result of a mandatory coal conversion pursuant to a Department of 

Energy Order under Section 301(c) of the Power Plant and Industrial Fuel Act of 1978 

(which superseded Sections 2(a) and (b) of the Energy Supply and Environmental 

Coordination Act of 1974)5. EPA has failed to consider Congresses intent with respect to 

this law. 

For the foregoing reasons, we believe it is clear that Sundt Unit 4 is not BART eligible. 

Additional Controls are not Required on Springerville Units 1 and 2 or Sundt Units 

1-3 to Meet Reasonable Progress Goals 

The Proposal includes a reasonable progress analysis with respect to S02 emissions on 

certain non-BART eligible sources including Springerville Generating Station 

("Springerville") Units 1 and 2 and Sundt Units 1-3 [77 FR 75729]. In each of these 

cases, EPA concluded that "it is not reasonable to require additional S02 controls" [77 

FR 75730]. TEP agrees with EPA's conclusion. 

Springerville Units 1 and 2 are equipped with spmy dryer absorbers (SDAs) for S02 

control, which operate at greater than 90-percent control efficiency. Furthermore, the 

SDAs for both units were upgraded as recently as 2006, which reduced the emission rate 

from these units to between 0.17 and 0.26 lbs!MBtu on an annual average basis. EPA's 

estimate of $17,000 to $22,000 per ton to install additional controls of is far beyond any 

reasonable threshold for cost effectiveness. EPA used an initial screening level of $5,000 

per ton to gauge cost effectiveness [77 FR 75729]. Note that TEP believes that a cost per 

ton of pollutant removed below this level could very well be not cost effective, and we 

encourage EPA to refrain from applying a generalized cost effectiveness threshold. Cost 

effectiveness should be considered site specifically and be weighed in reference to the 

2 40 C.F.R. Part 51 App. Y § II.A.2 (emphases added) 

3 70 FR 39111 

4 70 Fed. Reg. at 39111 

5 see 40 C.F.R § 52.21(b)(2)(iii)(b). 
EPA-R09-0AR-2012-0904 

March 6, 2013 

Page4 

other factors. Sundt Units 1-3 bum pipeline natural gas, and EPA correctly points out 

that "there are no cost effective controls" for such units. 

For point sources of NOx, EPA proposes to disapprove Arizona's finding that it is not 

reasonable to require additional controls on non-BART eligible point sources, because, in 

EPA's view, Arizona did not perform a thorough analysis. TEP believes that EPA's 

proper course of action should be to work with, and support the state in developing the 

analysis required for the evaluation of additional NOx controls on non-BART eligible 

sources. It is TEP's understanding that ADEQ is interested in addressing EPA's concerns 

about the adequacy of the analyses in their SIP, and therefore, it is premature for EPA to 

disapprove of the state's finding. 

If you have any questions regarding these comments, please feel free to contact me. 

Sincerely, 

�� 

Erik Bakken 

Director, Corporate Environmental Services 

and Land Management 

encl. 

cc: Mark Mansfield, TEP 

Phil Dion, TEP 

Eric Massey, ADEQ 
WILUAMS 

HuNToN& 

April 18, 2012 

Privileged and Confidential 

Attorney Work Product 

Colleen McKaughan 

Associate Director, Air Division 

United States Environmental Protection Agency 

Region IX 

75 Hawthorne Street 

San Francisco, CA 94105 

Dear Ms. McKaughan: 

HUNTON & WILLIAMS LLP 

2200 PENNSYLVANIA AVENUE, NW 

WASHINGTON, D.C. 20037-1701 

TEL 202 • 955 • 1500 

FAX 202 • 778 • 2201 

HENRY V. NICKEL 

DIRECT DIAL: 202 • 955 • 1561 

EMAIL: bnickel@hunton.com 

ALE NO: 37552.007 

We have been requested to respond to your letter of March 14,20 12, to Jeffrey Yockey 

regarding the BART-eligibility status of Unit 4 ofTEP's Sundt Generating Station under the 

visibility program of the Clean Air Act ("CAA"). TEP appreciates your interest in 

understanding the arguments that TEP intends to pursue in this matter. This response 

supplements the March 16, 20 11 email from Mr. Yockey to Francisco Donez addressing this 

issue and providing data regarding Unit 4's emissions, information on stack parameters for Unit 

4, and screening-level cost estimates for various categories of emission controls. 

We appreciate EPA's recognition, as stated in your letter, that the text ofEPA's BART 

Guidelines, which are codified rules at 40 C.F.R. Part 51 App. Y (hereinafter "Appendix Y") and 

thus are binding on EPA, expressly provide that "any emissions unit for which a reconstruction 

'commenced' after August 7, 1977, is not BART-eligible." 40 C.F.R. Part 51 App. Y § ll.A.2 

(emphases added). There is no dispute that Sundt Unit 4's reconstruction commenced after 

August 7, 1977. Moreover, Appendix Y contains no exceptions or qualifications to the broad 

exemption established by the rule quoted above. The footnote in the preamble to the BART 

Guidelines that you cite is not to the contrary, as it merely reflects the reality that post- 1977 

source reconstructions in the general run of cases would have "gone through NSRIPSD 

permitting." 70 Fed. Reg. 39 104, 39 111 n.9 (July 6, 2005). Nothing in that footnote does-- or 

ATLANTA AUSTIN BANGKOK BEUING BRUSSELS CHARLOTIE DALLAS HOUSTON LONDON LOS ANGELES 

McLEAN MIAMI NEW YORK NORFOLK RALEIGH RICHMOND SAN FRANCISCO TOKYO WASHINGTON 

www.hunton.com 
WIL

 HuNToN& 

Ms. Colleen McKaughan 

Aprill8,2012 

Page 2 

could -- contradict the plain, unqualified language of EPA's rule text that exempts "any" post1977 reconstruction. In any event, as EPA is aware, "[i]n the context of the CAA, 'the word 

"any'' has an expansive meaning.'" New Jersey v. EPA, 517 F.3d 574, 582 (D.C. Cir. 2008) 

(quoting New York v. EPA, 443 F.3d 880, 885 (D.C. Cir. 2006)). Likewise, while it is generally 

true that BART was intended to "apply to sources which had been 'grandfathered'" from NSR 

permitting requirements, 70 Fed. Reg. at 39111, it does not follow that BART applies either to 

all "grandfathered" sources (it does not apply, for example, to sources that were in operation 

before 1962) or to sources, like Sundt Unit 4, that were not grandfathered but instead were 

exempt from NSR permitting requirements as a result of a mandatory coal conversion pursuant 

to a Department of Energy Order under Section 301 (c) of the Power Plant and Industrial Fuel 

Act of 1978 (which superseded Sections 2(a) and (b) of the Energy Supply and Environmental 

Coordination Act of 1974), see 40 C.F.R § 52.21(b}(2)(iii)(b). (Because this order may have 

been the only one of its kind, a broader precedent is not presented by accepting TEP's argument.) 

For the foregoing reasons, we believe it is clear that Sundt Unit 4 "is not BART-eligible," 40 

C.F.R. Part 51 App. Y § ll.A.2, and thus cannot be subject to BART requirements. While TEP 

requests that EPA reconsider its position on the BART-eligibility of Sundt Unit 4, TEP 

understands that EPA may decide to evaluate BART factors as applied to Unit 4 while 

considering this request. If EPA intends to evaluate these factors for Unit 4, EPA must provide 

adequate time for development of relevant information and exchange of that information among 

EPA, the Arizona Department of Environmental Quality, and TEP, including information 

regarding visibility modeling and cost evaluations of alternative potential BART emission limits 

that might be considered for the unit. 

Unlike other sources in western states that have been evaluated for BART over the last two or 

more years, Unit 4 has not previously been identified as potentially subject to BART 

requirements. Thus, in contrast to other cases where potential BART emission limit 

determinations have been developed following extensive study and consultation, such study and 

consultation have not occurred with respect to Sundt Unit 4. Accordingly, unless EPA 

determines very soon (as it should) that Unit 4 is not BART-eligible-- or that, even if it is, it is 

not subject to BART -- TEP and the State of Arizona should be given an opportunity to provide 

information and input to EPA, and to react to EPA's information, views, and conclusions, on 

these matters. 
WI

 HuN'ION& 

Ms. Co11een McKaughan 

April18, 2012 

Page3 

Finally, TEP does not believe the provision of the pending proposed district court consent decree 

that would require proposed EPA action on regional haze implementation plan requirements for 

Arizona by May 15, 2012, and fmal EPA action by November 15, 2012, should be adopted. If, 

however, the decree is adopted and those dates are not significantly extended, then the decree 

should be revised to exclude Sundt Unit 4 from that provision's coverage, with later dates 

established for Unit 4 that would allow for resolution of the BART -eligibility issue (and the 

"subject to BART'' issue) for Unit 4 and development of necessary BART-related information 

with respect to the unit. 

We would be happy to discuss these matters with you further at your convenience. 

I� 

cc: , EPA Region IX 

ric Mass , Arizona Department of Environmental Quality 

Marc Jerden, Esquire, TEP 

Erik Bakken, TEP 

Jeffrey G. Yockey, P.E., TEP 
ATTACHMENT B 
� 

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Sundt Unit 4 - 2011 Gross Load 

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02/20/1 1 04/1 1 /11 05/31/1 1 07/20/11 09/08/1 1 1 0/28/1 1 1 2/1 7/1 1 

Date 
ATTACHMENT C 
May 9, 20 13 

Mr. Jeffrey G. Yockey, P.E. 

Manager, Corporate Environmental Services 

UniSource Energy Corporation 

Mail Stop HQW602 

88 E Broadway Blvd 

Tuscan, AZ 85702-07 11 

Re: Tucson Electric Power Sundt Unit 4 BART Rev iew 

Dear Mr. Yockey: 

Burns & McDonnell has performed a review of the draft Five-Factor BART Analysis1 for the 

TEP Sundt Station Unit 4 that was prepared for US EPA Region 9 and issued October 9, 20 12. 

Our analysis reviewed the capital and operating costs for each technology and identified 

differences between our estimate and the estimates prepared for Region 9. 

Burns & McDonne ll's estimate of the control costs was higher for all technology applications 

than the estimates prepared for Region 9. The estimated removal costs per ton by control 

technology are summarized in Table No. I. 

Table No. 1 

Control Cost Estimate Summary 

Region 9 BART BMcD 

Estimates Estimates 

NOx Control Technology 

Selective Non-Catalytic Reduction (SNCR) $ 3,295 $ 3,637 

Selective Catalytic Reduction (SCR) $ 4,874 $ 7,874 

S02 Control Technology 

Dry Sorbent Injection $ 1,826 $ 3,088 

Dry FGD $ 6,434 $ 9,359 

Wet FGD $ 6,957 $ 8,229 

Note: Atf values are in $/ton of pollutant removed 

1 Technical Analysis for Arizona and Hawaii Regional Haze FIPs: Task 7: Five-Factor BART Analysis for TEP 

Sundt (Irvington), Contract No. EP-D-07-102, Work Assignment 5-12, Version 1, October 9, 2012 

9400 Word Parkway • Kansas (ify, Missouri 64114-JJ/9 

Tel: 816-JJJ-9400 • fox.· 816-JJJ-3690 • www.hurnsmcd.com 
May 9, 201 3 

Page 2 

The estimates prepared for Region 9 were based on average inlet pollutant loadings for 20 1 1. 

The 201 1 data is a good basis as Unit 4 was operated on coal for a large percentage of the time. 

However, the EPA analysis assumes a Unit 4 gross generating capacity of 173 .3 MW. This is 

the unit's gross generating capability on natural gas. The unit cannot reach this load while firing 

coal. The unit is limited to approximately 130 MW when firing coal. 

The EPA analysis determined a capacity factor for the unit of0 .37 based on the capability of 

Unit 4 to achieve 1 73 .3 MW on natural gas. A more appropriate capacity factor, using a 1 30 

MW gross generating capability while firing coal, is 0 .49 based on the 20 11 data. (Please note 

that although the calculated capacity factor is different, the annual emissions in tons per year 

removed do not necessarily change significantly. The change in capacity factor is largely offset 

by the change in maximum unit gross rating.) 

Following is a summary of the cost estimates for each technology that was evaluated in the 

report prepared for Region 9 and a discussion of the reasons for the differences from the Burns & 

McDonnell estimates. 

NOx CONTROLSYSTEMS 

Selective Non-Catalytic Reduction CSNCR) 

The BART analysis prepared for Region 9 determined a NOx removal cost to be approximately 

$3300 per ton for installation, operation and maintenance of a SNCR system on Unit 4. Burns & 

McDonnell's analysis indicated the costs should be higher at approximately $3640 per ton of 

N Ox removed (based on 201 1 operating data). The results of these analyses are provided in 

Table No. 2. 

2 
May 9, 201 3 

Page 3 

Table No. 2 

SNCR Cost Comparison 

Capacity Factor 

Control Efficiency 

U ncontrolled Rate 

NOx Rate lbs/hr 

NOx Rate lbs/mmBtu 

NOx (tpy) 

Controlled 

NOx Rate (lbs/hr@ rated load) 

NOx Rate (lbs/mmBtu) 

NOx (tpy) 

NOx Removed (tpy) 

Costs 

Fixed O&M $ 

Variable O&M ($) 

Total O&M ($) 

Capital Cost 

Capital Cost (annualized) 

Total Annual Cost 

Cost ($/ton Nox Removed) 

BART Report 

0.37 

30% 

813 

0.445 

1318 

569 

0.31 

923 

395 

97,048 

842,550 

939,598 

3,446,000 

361,850 

1,301,448 

3,295 

BMcD Estimate 

0.49 

30% 

610 

0.445 

1367 

427 

0.31 

957 

410 

193,800 

807,684 

1,001,484 

4,695,000 

490,158 

1,491,642 

3,637 

There are several reasons for the difference in the cost estimates. These are summarized below: 

• Capital Costs: Differences in capital costs is the primary factor that influenced the 

overall estimates. Burns & McDonnell's estimate of the installed SNCR costs was 

approximately 35 percent higher than the estimate prepared for the EPA. There are 

several reasons that the costs estimated for the EPA are lower: 

• 

o The EPA estimate includes only $1 7/kw for the SNCR and balance of plant costs. 

This is lower than the $1 8/kw than was provided in the Integrated Planning Mode l 

{IPM) repore which is refe renced in the Five-Factor BART analysis as the basis 

for the estimate. 

2 Documentation for EPA Base Case v.4.10 Using the Integrated Planning Model, United States Environmental 

Protection Agency, Air and Radiation, EPA @ 430RIOOI 0, August 2010 

3 
May 9, 2013 

Page4 

o The IPM report costs are in 2010 dollars and need to be escalated to the current 

year. These adjustments would add approximately $400,000 to the estimated 

capital cost. 

o The factors used to account for engineering and other issues appear low in the 

Region 9 estimate. For example, the estimate included only 5 percent total for 

engineering and construction management. This is far below the values listed in 

the referenced IPM manual. The engineering and construction management costs 

should be in the 20 percent range. Adjusting for this issue would add 

approximately $500,000 to the estimate. 

o The EPA estimate assumed that a removal of 30 percent can be maintained with 

an SNCR. Continually achieving this high removal efficiency requires the 

instal lation of multiple SNCR spray levels and the associated piping and controls 

to al low for variations in unit operation and load. The urea must be sprayed into 

the appropriate temperature zone in the steam generator to achieve satisfactory 

performance. Installing multiple spray levels adds significantly to the SNCR 

costs. 

• 

• Fixed Operating & Maintenance Costs: The fixed operating costs in the estimate 

prepared for Region 9 included only $97,000 for annual O&M. Most of this cost was for 

additional operations personnel. This estimate is not adequate for a system that includes 

silos unloading equipment, transfer and distribution equipment, numerous control valves 

and multiple injection levels. The maintenance costs should be at least 2 percent of the 

capital costs which adds approximately $100,000 to the fixed O&M costs. 

• Variable Operating Costs: The variable operating costs were reasonably close between 

the estimates. 

NOx CONTROLSYSTEMS 

Selective Catalytic Reduction (SCR) 

The estimates to install and operate an SCR system on Sundt Unit 4 were substantially different. 

The estimate prepared for Region 9 was approximately $4900 per ton ofNOx removed. Burns 

& McDonnell's estimate was approximately $7900 per ton removed. A summary of the 

estimates is provided in Table No.3. 

4 
May 9, 2013 

Page 5 

Table No.3 

SCR Cost Comparison 

BART Report 

Capacity Factor 0.37 

Control Efficiency 89% 

Uncontrolled Rate 

NOx Rate lbs/hr 813 

NOx Rate lbs/mmBtu 0.445 

NOx (tpy) 1318 

Controlled Emissions 

NOx Rate (lbs/hr@ rated load) 91 

NOx Rate (lbs/mmBtu) 0.05 

NOx (tpy) 148 

NOx Removed (tpy) 1170 

Costs 

Fixed O&M $ 362,000 

Variable O&M ($) 1,376,165 

Total O&M ($) 1,738,165 

Capital Cost 37,970,000 

Capital Cost (annualized) 3,964,068 

Total Annual Cost 5,702,233 

Cost ($/ton Nox Removed) 4,874 

BMcD Estimate 

0.49 

89% 

610 

0.445 

1367 

67 

0.05 

150 

1217 

739,200 

935,000 

1,674,200 

75,720,000 

7,905,168 

9,579,368 

7,874 

The difference in the estimated capital costs was the primary factor that influenced the costs to 

remove a ton ofNOx. Burns & McDonnell believes this difference in estimated capital costs is 

because the estimate prepared for the EPA did not take into account the extreme difficulty of 

install ing an SCR on Unit 4 given site specific factors (The EPA estimate used a capital costs 

retrofit factor of 1.0). 

The Sundt facility is extremely congested and substantial additional costs will be incurred with 

the installation of an SCR for the unit. Even the feasibility of installing an SCR on Sundt 4 is 

questionable. An extensive study will be required to evaluate the feasibility of install ing SCR 

before a final decision regarding the technology can be made. 

5 

• 
May 9, 2013 

Page 6 

• 

Potential options that could be considered for the SCR include installing the SCR in a "tailend" 

configuration or replacing the existing air heaters. However, both of these solutions would be 

substantially more expensive than any of the estimates provided in this report. 

Some of the factors that make the SCR installation extremely difficult include: 

• An SCR cannot be installed in a truss arrangement above the air heater (the common 

SCR retrofit configuration) due to the existing boiler structure and interferences with the 

existing coal handling system. 

• The exiting Unit 4 air heater is a horizontal shaft configuration located at a very low 

elevation. The ductwork from the economizer outlet to the air heater is completely 

encompassed by boiler steel and other structures. This makes routing ductwork from the 

economizer outlet to the SCR and back to the air heater inlet (as would be required with 

a "side-saddle" SCR arrangement) very difficult or impossible. Exhibit 1 shows the 

congestion in this area. 

• Material handling systems (primarily coal handling) completely block the air heater area 

on three sides of Unit 4 and partially blocks the area on the fourth side. The material 

handling systems cannot be relocated due to site constraints. The material handling 

systems interference greatly complicates locating the SCR and routing ductwork to and 

from the SCR. 

• The Unit 3 circulating water lines run adjacent to the north side of the Unit 4 boiler area 

where it appears an SCR could be located. Consequently, the SCR will have to be 

located remote from the unit adding substantially to the SCR costs. Exhibit 2 illustrates 

the impact the Unit 3 circulating water lines have on the installation of a Unit 4 SCR. 

The difference in the predicted control costs prepared for Region 9 and those prepared by Burns 

& McDonnell is 34 percent. There are several reasons for this difference which are summarized 

below. 

• Capital Costs: Burns & McDonnell's estimate of the capital costs to install SCR on Unit 

4 was approximately twice the estimates prepared for Region 9. Items that we believe 

impact the estimated costs include: 

o The Region 9 estimate used a retrofit factor of 1 .0 for the SCR installation. As 

discussed above, the installation of an SCR on Sundt Unit 4 would be extremely 

difficult if it is even feasible. The area around the Unit 4 boiler is very congested 

with ductwork, coal handling equipment and the fabric filter. The SCR will have 

to be located some distance away from the air heater gas inlet requiring 

substantial additional ductwork compared to a normal installation. Equipment 

and instal lation costs to instal l an SCR on the unit will be substantially greater 

6 
May 9, 2013 

Page 7 

than the capital cost estimate prepared for Region 9. Using a retrofit factor of I .5 

or higher is appropriate for this application. 

o The EPA estimate did not include any costs for air heater modifications. 

Substantial modifications to the air heater will be needed to accommodate SCR 

operation. The minimum modifications (sootblower addition) to the air heater 

would add $ I-2 million to the base capital costs. 

• 

o The estimated base SCR costs prepared for Region 9 seems low and does not 

appear to take into account the size of the unit in determining the capital costs. 

The direct capital cost of $2 I6 per kw from the Region 9 estimate was only 

slightly more than the costs for a 600 MW unit. Industry experience is that the 

unit cost ($ /kw) of installing an SCR on a small unit will be much more expensive 

than the unit cost of an SCR installation on a large unit. Cichanowicz3 reported, 

based on a survey of SCRs installed in the 200 8-20 I 0 time frame, the unit costs 

for a unit similar in size to Sundt 4 would be around $350 per kw. Burns & 

McDonnell's experience in recent years is that direct costs for an SCR on a small 

unit can easily exceed $400 per kw (assuming a normal retrofit application). 

o The cost estimate is based on the IPM report which is in 20 IO dollars. The capital 

costs should be escalated to the current date which adds approximately 5-I 0 

percent to the costs. 

o The Region 9 estimate did not inc! ude Owner's costs. Owner's costs of at least 5 

percent should be added. 

• Fixed Operating Costs: The fixed operating costs in the estimate prepared for Region 9 

included approximately $300 ,000 for annual maintenance. This estimate seems 

extremely low for a system ofthis cost and complexity. Burns & McDonnell believes 

this cost should be at least I percent ofthe capital cost which using a realistic capital cost. 

Using a realistic percentage would add approximately $400 ,000 per year to the fixed 

operating cost estimate. 

• Variable Operating Costs: Burns & McDonnell's estimate for the variable operating 

costs was substantially lower than the estimates prepared for Region 9. This appears to 

be because variable cost estimate for Region 9 included a high cost for catalyst disposal 

(We assume this cost also includes replacement catalyst.) The Region 9 estimate 

included nearly $ 600 ,000 per year for catalyst replacement. A more appropriate average 

catalyst replacement cost would be around $300 ,000 per year for Unit 4. 

3 Current Capital Cost and Cost-effectiveness of Power Plant Emisssions Control Technologies, J. Edward 

Cichanowicz, Prepared for Unitility Air Regularoty Group, January, 2010 

7 
May 9, 2013 

Page 8 

SO& CONTROL SYSTEMS 

Dry Sorbent Injection (DSI) 

The costs to install and operate a DSI system on Unit 4 are summarized in Table No. 4. The 

projected cost in the estimates prepared for Region 9 was approximately $1 800 per ton of S02 . 

Burns & McDonnell's estimate for the DSI costs was approximately $3100 per ton removed. 

Table No. 4 

DSI Cost Comparison 

Capacity Factor 

Control Efficiency 

Uncontrolled Rate 

S01 Rate lbs/hr 

S01 Rate lbs/mmBtu 

so2 (tpy) 

Controlled Emissions 

S02 Rate (lbs/hr@ rated load) 

S02 Rate (lbs/mmBtu) 

S02 (tpy) 

502 Removed (tpy) 

Costs 

Fixed O&M $ 

Variable O&M ($) 

Total O&M ($) 

Capital Cost 

Capital Cost (annualized) 

Total Annual Cost 

Cost ($/ton S02 Removed) 

BART Report 

0.37 

75% 

1333 

0.729 

2160 

333 

0.18 

540 

1620 

164,000 

2,342,289 

2,506,289 

4,332,000 

452,261 

2,958,550 

1,826 

BMcD Estimate 

0.49 

70% 

999 

0.729 

2160 

599 

0.22 

648 

1512 

238,600 

3,701,000 

3,939,600 

6,980,000 

728,712 

4,668,312 

3,088 

There are a variety of reasons for the difference in the cost estimates. These are summarized 

below: 

• S02 Control Level: The estimated removal for the Region 9 estimate was 75 percent. 

This control level is high, particularly considering the low capacity factor for the unit. 

8 
May 9, 2013 

Page 9 

We believe a more appropriate S02 control level would be around 70 percent for DSI on 

Unit4. 

• Capital Costs: Burns & McDonnel l's estimate of the instal led DSI costs was 

approximately twice the estimate prepared for the EPA. It appears the basis for the 

estimate was an arbitrary $ 25/kw. While this value may be appropriate for larger units, 

the unit costs ($ /kw) would be significantly higher for a small unit such as Sundt 4. 

There were a few additional issues that would impact the capital costs of installing a DSI 

system: 

o The Region 9 estimate included only 5 percent for engineering and construction 

management and no Owner's costs. Appropriate values would add 15 to 20 

percent to the estimate. 

o The costs did not include any balance of plant costs. A DSI system will require 

instrument air and other services. 

o The Sundt site is very congested. It is likely the sorbent silos will need to be 

located some distance from the injection point. This will add to the capital costs 

due to the increased length of transfer piping. 

• 

• Fixed Operating Costs: The fixed operating costs in the estimate prepared for Region 9 

included only $36,000 for annual maintenance material and labor costs. This value is not 

adequate for a DSI system which includes silos, transfer blowers, piping and valves, and 

multiple injection nozzles. A cost of at least 1-2 percent of the capital costs should be 

included which would be approximately $100 ,000. 

• Variable Operating Costs: Burns & McDonnell's estimate of the variable operating costs 

is approximately $1 .3 million higher than the Region 9 estimate. The Region 9 estimate 

appears to be based on using lime as the sorbent. Burns & McDonnell's estimate is based 

on using a sodium based sorbent. We believe it is more appropriate to use a sodium 

sorbent considering the high S02 removal levels required for the project. 

DryFGD 

The projected costs to install and operate a dry FGD on Unit 4 are summarized in Table No. 5. 

Burns & McDonnell's cost for the dry FGD (including a new fabric filter) is approximately 45 

percent higher than the estimates prepared for Region 9. 

9 
May 9, 2013 

Page 10 

Table No. 5 

Dry FGD Cost Comparison 

BART Report 

Capacity Factor 0.37 

Control Efficiency 89% 

Uncontrolled Rate 

502 Rate lbs/hr 1333 

502 Rate lbs/mmBtu 0.729 

502 (tpy) 2160 

Controlled Emissions 

502 Rate (lbs/hr @ rated load) 146 

502 Rate (lbs/mmBtu) 0.08 

502 (tpy) 237 

502 Removed (tpy) 1923 

Costs 

Fixed O&M $ 2,067,000 

Variable O&M ($) 1,011,000 

Total O&M ($) 3,078,000 

Capital Cost 89,034,000 

Capital Cost (annualized) 9,295,150 

Total Annual Cost 12,373,150 

Cost ($/ton 502 Removed) 6,434 

BMcD Estimate 

0.49 

89% 

999 

0.729 

2160 

110 

0.08 

237 

1923 

3,058,000 

792,000 

3,850,000 

135,520,000 

14,148,289 

17,998,289 

9,359 

Following is a discussion of the differences between the cost estimates: 

• Capital Costs: Burns & McDonnell's estimate of the installed dry FGD costs was 

approximately 50 percent higher than the estimate prepared for the EPA. The scope of 

work was similar for both estimates including the dry FGD, a new fabric filter, auxiliary 

systems and balance of plant equipment. Several issues were identified that account for 

much ofthe difference. 

o The Region 9 estimates included a retrofit factor of 1 .0 for the dry FGD system. 

• 

The site around Unit 4 is very congested. Due to the location of the Unit 3 

circulating water lines and other equipment, a dry FGD and fabric filter could not 

be located immediately adjacent to Unit 4. There is space behind Unit 3 (where a 

gas turbine was previously installed) that could potentially be used. However, the 

10 
May 9, 2013 

Page 11 

available area is limited, which will make it difficult to install a new dry FGD, 

fabric filter, and ID fan. It may be necessary to install reagent preparation or 

other equipment at a remote location. With these complications, a more 

appropriate retrofit factor would be 1.2 or 1 .3. 

o The EPA cost estimates were based on the IPM report which is in 20 10 dollars. 

These costs should be escalated to current dollars which would add 5 to 10 

percent to the costs. 

o The estimates did not include any Owner's costs. Owner's costs of at least 5 

percent should be included. 

• Fixed Operating Costs: The fixed operating costs in the estimate prepared for Region 9 

was approximately 67 percent of the Burns & McDonnell estimate. This was primarily 

due to using lower maintenance material and labor costs. The estimate prepared for the 

EPA has a fixed maintenance and material cost of slightly over 1 percent of capital costs. 

For a complex system such as a dry FGD with fabric filter, the costs should be in the 

range of 2-3 percent. 

• 

• Variable Operating Costs: Burns & McDonnell's estimate of the variable operating costs 

was approximately 30 percent lower than the Region 9 estimate. We believe much of the 

difference is due to the auxiliary power consumption which appears to be high in the 

Region 9 estimate. The Region 9 estimate includes approximately $500 ,000 per year in 

auxiliary which corresponds to 1 200 operating hp. We believe the actual additional 

usage attributed to the dry FGD would be around 900 hp. 

Wet FGD 

A summary of the capital and O&M cost estimates associated with installing a wet FGD is 

provided in Table No 6. 

II 
May 9, 2013 

Page 12 

Table No. 6 

Wet FGD Cost Comparison 

BART Report 

Capacity Factor 0.37 

Control Efficiency 92% 

Uncontrolled Rate 

502 Rate lbs/hr 1333 

502 Rate lbs/mmBtu 0.729 

502 (tpy) 2160 

Controlled Emissions 

502 Rate (lbs/hr @ rated load) 110 

502 Rate (lbs/mmBtu) 0.06 

502 (tpy) 178 

502 Removed (tpy) 1982 

Costs 

Fixed O&M $ 2,700,000 

Variable O&M ($) 747,000 

Total O&M ($) 3,447,000 

Capital Cost 99,058,000 

Capital Cost (annualized) 10,341,000 

Total Annual Cost 13,788,000 

Cost ($/ton 502 Removed) 6,957 

BMcD Estimate 

0.49 

92% 

999 

0.729 

2160 

80 

0.06 

178 

1982 

2,812,000 

763,000 

3,575,000 

121,990,000 

12,734,949 

16,309,949 

8,229 

Bums & McDonnell's estimated S02 removal cost is approximately 18 percent higher than the 

estimates prepared for Region 9. Fol lowing is a discussion for the reasons. 

• Capital Costs: Bums & McDonnell's estimate of the installed wet FGD costs was 

approximately 20 percent higher than the estimate prepared for the EPA. There are 

several reasons for the difference: 

o The estimates prepared for the EPA included a retrofit factor of 1 .0. The use of a 

1 .0 retrofit factor assumed that the absorber could be located immediately east of 

the existing fabric filter. However, the Unit 3 circulating water lines are located 

immediately east of the Unit 4 fabric filter. Consequently, the area is not totally 

available for installation of a FGD system. The FGD tower could potentially be 

12 

• 
May 9, 20 13 

Page 13 

located in this limited area, however, the reagent preparation and waste treatment 

systems would likely have to be located remote. Space would also be needed for 

a new ID fan. Considering these issues, a more appropriate wet FGD retrofit 

factor for Unit 4 is 1.1 or 1 .2. 

o The existing fabric filter discharge is to the west. With a wet FGD system, the 

fabric filter would need to be reconfigured to discharge to the east. This is 

another reason the retrofit factor should be increased as discussed above. 

o The EPA estimate did not include Owner's costs. Owner's costs of 5 percent 

should be included. 

• Fixed Operating Costs: The total fixed operating costs were similar for the two 

estimates. The Region 9 estimate included more operating labor which was offset by a 

higher estimate of maintenance materials and labor costs in the Burns & McDonnell 

estimate. 

• Variable Operating Costs: The variable operating costs were similar between the 

estimates. 

CONCLUSION 

• 

Burns & McDonnell reviewed the cost estimates prepared for the EPA Region 9 dated October 9, 

20 12. For all technology cases, the estimates prepared for Region 9 were lower than Burns & 

McDonnell would expect for the Sundt Unit 4. Most of the cost variance was due to differences 

between the capital cost estimates. 

Please advise if you have any questions or comments or if you require additional information. 

Sincerely, 

� A- .� 

Stephen A. Bjorklun, P.E. 

Senior Associate Process Engineer 

Energy Group 

Burns & McDonnell Engineering Company 

Enclosures 

cc: Joey Mashek 

Block Andrews 

13 
COPYRIGHTC 2013 BURNS & McDONNELL ENGINEERING COMPANY, INC 

AIR HEATER ri 'ft 

U:\MECHDEPn1 111 \CADD\MECH\73483-BJORKLUN\EXHIBIT 1 .DWG 5/8/201 3 1 :34 PM MATHERTON 

AIR H EATER 

GAS INLET 

TEP SUNDT UNIT 4 

EXH IBIT 1 

AIR H EATER AREA 

GAS INLET DUCT 
COPYRIGHTCI 2013 BURNS & McDONNELL ENGINEERING COMPANY, INC. 

POTENTIAL SCR 

LOCATION ------' 

UNIT 3 CIRCULATING 

WATER LINES ---' 

U :\MECHDEPl\1 111 \CADD\MECH\73483-BJORKLUN\EXHIBIT 2.DWG 5/8/2013 1 :41 PM MATHERTON 

TEP SUNDT UNIT 4 

EXH I BIT 2 

SITE PLAN 
ATTACHMENT D 
A:COM 

Environment Prepared for: 

Tucson Electric Power 

Tucson. AZ 

Prepared by: 

AECOM 

Chelmsford, MA 

60278385.100 

May 2013 

Visibil ity I mprovement Analysis for 

Candidate BART Control Options: 

Sundt U nit 4 
AS'COM Environment Prepared for: 

Tucson Electric Power 

Tucson, AZ 

Prepared by: 

AECOM 

Chelmsford, MA 

60278385.100 

May 201 3 

Visibil ity I mprovement Analysis for 

Candidate BART Control Options: 

Sundt U nit 4 

rt J. Paine and Olga Samani 

Reviewed By 
AECOM Environment 

Contents 

Executive Summary ........................... ................ ........................................................ ES-1 

1 .0 lntroduction .................................................................................................................... 1 -1 

1 .1 Background ...... ........... ...................... ....... ................... ............................. ............... ............. 1 -1 

1 .2 Organization of Report ........... . .......... . ........ .................................................. . . ...................... 1 -1 

2.0 Sundt Plant Description and Nearby Class I Areas .................................................... 2-1 

3.0 BART Emission Cases .................................................................................................. 3-1 

3.1 BART Option 1: Dry Sorbent Injection (DSI) for S02 Controls and SNCR NOx Controls. 3-1 

3.2 BART Option 2: Dry Scrubber for S02 and H2S04 Controls and SCR NOx Controls .... . . . 3-1 

4.0 CALPUFF Modeling Procedures .................................................................................. 4-1 

4.1 CALPUFF Model Formulation for Predicting Visibility Impairment ............................... ..... 4-1 

4.2 Ammonia Background Concentrations ............ . . . ............................. . ... ..... . ....................... . . 4-1 

4.3 CALMET Modeling Procedures ........................ . . ................ .............. . . . . .... . . ...................... . . . 4-4 

4.4 CALPOST Post Processor and Deciview Calculations ............ ...... . . . . ..... . ............... ........ ... 4-4 

4.5 CALPUFF Modeling Procedures ...................... . . .... ............. ............ . ... ..... . ....................... ... 4-5 

5.0 Visibility Improvement Modeling Results ................................................................... 6-1 

5.1 Baseline Emissions Modeling Results for BART Screening ............ . ...... . ............ . . . . .... . ... . . 5-1 

5.2 BART Control Option Visibility Modeling Results .... ................................. . ........... . ... .... . ... . . 5-2 

5.3 Visibility Improvement Effectiveness Metrics . . ... ........................... ............ . ........ .... . . . ........ . . 5-2 

5.3.1 Magnitude of Minimum Visibility Improvement ................ ....... . ............... ....... . . . .. . 5-2 

5.3.2 Visibility Improvement Cost Effectiveness ............. ............ . . ...... . ........... . . . . . ... . . . . . . 5-3 

5.3.3 Visibility Modeling Results ..... . ...... .... . . . ................. .............. . . ................... ......... .. . . 5-4 

6.0 Conclusions ................................................................................................................... 6-1 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment ii 

List of Appendices 

Appendix A Visibility Modeling Results for All Class I Areas 

List of Tables 

Table 3-1 : Unit 4 Exhaust Stack Parameters ..................... . .. . . ... . .. .. . . .................................................. 3-2 

Table 3-2: Emissions and Stack Parameters for Sundt Units 1 -4 .. .................................................... 3-3 

Table 4-1 : Background Monthly Ammonia Concentrations Used in the Modeling (ppb) ...... ............ 4-4 

Table 5-1 : 981h Percentile Baseline Case CALPUFF Modeling Results* for Visibility Impairment, 

delta-deciview ................................................... . ............... ................. .............................. ... 5-1 

Table 5-2: Visibility Improvement* over Baseline Conditions, delta-deciview ................................... 5-2 

List of Figures 

Figure 2-1 : Photograph of the TEP Sundt Facility ........ ............... ........... ................................. ............ 2-1 

Figure 2-2: Class I Areas Within 300 km of TEP Sundt... ..... ............ ..... ....... .............. . . ....................... 2-2 

Figure 4-1 : IMPROVE NHx Concentrations from April 201 1 to January 201 2 ............... ........ ... ......... 4-3 

Figure 4-2: 2009 IMPROVE Composition Data for Saguaro West National Park ("SAWE1") and 

Saguaro East National Park ("SAGU1 ") ................................. . . . . .. .... . ...... . ... ... . .. . ... .... ... . . . . . 4-3 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment ES-1 

Executive Summary 

The United States Environmental Protection Agency (EPA) Region 9 is anticipated to focus in the near 

future upon a Best Available Retrofit Technology (BART) evaluation for the Sundt Unit 4, which can be 

fired with either coal or natural gas and is located in Tucson, Arizona. Tucson Electric Power 

Company (TEP) does not believe Sundt Unit 4 is BART eligible, however, TEP has asked AECOM to 

review the BART analysis conducted for EPA 1 and to provide a visibility assessment for two emission 

control options for this coal-fired unit: 

• S02 control using dry sorbent injection (providing 70% control over the baseline emission 

rate), and NOx control using Selective Non-Catalytic Reduction (providing 30% control over 

the baseline emission rate). 

• S02 control using dry flue gas desulfurization ("dry scrubbing", providing 89% control), and 

NOx control using Selective Catalytic Reduction (providing 89% control). 

As a result of this review, AECOM has conducted new modeling with the following changes from 

EPA's modeling: 

• Updated stack parameters for Unit 4 were modeled based on revised exhaust parameters 

provided by TEP. 

• TEP estimated a revised (70%) control efficiency for the dry sorbent injection (DSI) S02 

emission controls, slightly lower than what EPA used (75%). 

• Based upon newly available ammonia measurement information, AECOM used as input to 

CALPUFF a set of monthly-varying ammonia background concentrations that correspond to 

the actual measured values during winter at a Class I area being modeled in southern 

Arizona, which range from 0.5 to 1 .0 ppb. EPA had applied a 1 .0 ppb ammonia value for all 

months of the year. 

A visibility improvement modeling review was conducted for all Prevention of Significant Deterioration 

Class I areas within 300 km of the plant, using the CALPUFF model version 5.8. This model has a 

known over-prediction bias for nitrate haze formation that overstates the visibility improvements for the 

candidate BART options. The modeling also does not account for the haze-causing effects of 

ammonia slip from the NOx emission controls that were evaluated. 

The results of the analysis indicate even with the model overprediction biases, the only Class I area 

with 981h percentile daily impacts above the BART contribution to haze screening level of 0.5 deltadeciview is Saguaro National Park. Even at this park, the candidate controls result in levels of visibility 

improvement that are too low to be detected by the available technology for particulate monitors (well 

below the measurement threshold of 0.3 delta-deciview), and they are less than 20% of the 

perceptible levels that can be visually detected (1 deciview). Furthermore, the cost effectiveness of 

both of the control options is higher than the Federal Land Manager-established benchmark of $20 

million/dv. Accordingly, we conclude that neither of these control options would provide cost-effective 

visibility improvement and therefore it is not reasonable to require additional controls of S02 or NOx at 

Sundt Unit 4. 

1 Technical Analysis for Arizona and Hawaii Regional Haze FIPs: Task 7: Five-Factor BART Analysis for TEP 

Sundt (Irvington). EMAQ LOE (EPA Contract EP-D-07-102). October 9, 2012. 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 201

3 
AECOM Environment 1 -1 

1 .0 I ntroduction 

1 .1 Background 

Even though TEP has shown that Sundt Unit 4 is not BART eligible, The United States Environmental 

Protection Agency (EPA) Region 9 is anticipated to focus in the near future upon a BART evaluation 

for Sundt (formerly Irvington) Unit 4, which can be fired with either coal or natural gas and is located in 

Tucson, Arizona. 

TEP has asked AECOM to review Sundt Unit 4 BART report and modeling prepared by the Institute 

for the Environment, IFC International, and Andover Technology Partners for EPA2

. As a result of this 

review, AECOM has conducted its own modeling that used the EPA-provided modeling as a starting 

point. However, the updated modeling documented in this report uses newly available information on 

stack parameters, control efficiencies, and ammonia background input to CALPUFF that was not 

available to EPA when they conducted their analysis. 

AECOM has incorporated these refinements into a visibility assessment for two emission control 

options for Unit 4 that were described in the EPA report: 

• Option 1: Coal-fired operation with BART controls consisting of dry sorbent injection (DSI) 

controls for S02, and selective non-catalytic reduction (SNCR) controls for NOx emissions. 

• Option 2: Coal-fired operation with BART controls consisting of spray dryer absorber ("dry 

scrubbing") controls for S02 and sulfuric mist (H2S04) emissions, and selective catalytic 

reduction (SCR) controls for NOx emissions. 

This study provides an updated comparison of the relative benefits of the two different control options 

compared to baseline conditions with current emission controls. 

This visibility assessment has been carried out using CALPUFF modeling approaches consistent with 

those used by the Arizona Department of Environmental Quality (ADEQ) for their BART visibility 

modeling. Our review of the comparative visibility benefits addresses the benefits offered by the two 

emission control options. 

1 .2 Organization of Report 

Section 2 of this report provides a description of the Sundt plant and the Prevention of Significant 

Deterioration (PSD) Class 1 areas within 300 km. Section 3 discusses the baseline emissions as well 

as the emissions associated with the two control options that have been modeled. Section 4 provides 

the procedures used in the CALPUFF modeling. Section 5 presents the results of the modeling and 

Section 6 provides the conclusions of the study. 

2 Technical Analysis for Arizona and Hawaii Regional Haze FIPs: Task 7: Five-Factor BART Analysis for TEP 

Sundt (Irvington). EMAQ LOE (EPA Contract EP-D-07-102). October 9, 2012. 

Vlsibllity Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 

2.0 Sundt Plant Description and Nearby Class I Areas 

2-1 

Tucson Electric Power Company operates the Sundt Generating Station ("Sundt"), which is located in 

Tucson, Arizona, approximately 2 miles northeast of Tucson International Airport. Figure 2-1 shows a 

photograph of the plant. 

Figure 2-1 : Photograph of the TEP Sundt Facility 

There are ten Class I areas within 300 km (the distance to which BART visibility assessments are 

typically done) of the source, as shown in Figure 2-2. They are: Mazatzal Wilderness Area, Gila 

Wilderness Area, Mt. Baldy Wilderness Area, Sierra Ancha Wilderness Area, Galiuro Wilderness 

Area, Superstition Wilderness Area, Pine Mountain Wilderness Area, Chiricahua Wilderness Area, 

Chiricahua National Monument, and Saguaro National Park. Saguaro National Park has two districts 

- east and west that are separated by the City of Tucson. Since Sundt is located between the east 

and west district. initial modeling was considered for each district separately to determine which 

district has the higher impacts. 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 2-2 

Figure 2-2: Class I Areas Within 300 km of TEP Sundt 

Mexico 

Pine Moun

Q 

MBZatzal WlldarnessV. Wil erness 

'i. Sierra Ancha 

c.l Wilderness 

t: 

Mount Bal y 

Arizona 

legend 

-tr TEP 

Scala 

0 

r- SUperstition 

Wilderness 

Wil erness 

fl Galluro � Wlldam SI 

� 

Saguaro* l:J Wast NP Saguaro 

East NP 

Mexico 

Chlrlcahua NM 

& Chlrlcahua � 

Wilderness Y 

Tucson Electric Power 

37.5 75 

Class I Areas Within 300 km 

ofTEP Sundt 

150 225 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 

New Mexico 

A: COM 

May 2013 
AECOM Environment 

3.0 BART Emission Cases 

This section discusses the baseline emissions as well as the emissions associated with the two 

candidate BART control options that have been modeled. The modeled stack parameters for the 

baseline coal-firing case and the control options for coal firing are listed in Table 3-1 . 

Unit 4 Baseline Case 

3-1 

Table 3-2 provides the emissions for S02, NOx, and species of particulate matter (the required 

constituents needed for visibility improvement modeling) for the baseline coal-firing case. The 

baseline emissions are the same as those used in EPA's modeling, which are calculated from the 

peak daily emissions for S02 (corresponding to 0.723 lb/MMBtu and 30,950 MMBtu heat input) and 

NOx (corresponding to 0.434 lb/MMBtu and 30,950 MMBtu heat input) as derived from continuous 

emission monitors, and from the peak daily heat input rate and data from stack testing for PM10 

emissions. The peak daily baseline emissions for S02 and NOx occurred on 1 /1 1/2008. Consistent 

with EPA's modeling, we have included Sundt Units 1 -3 as well as Unit 4 in all modeled cases. Since 

Units 1 -3 are not subject to BART, the emissions for these units were kept the same for all cases 

modeled for Unit 4. Tucson Electric specified slightly updated exhaust parameters (relative to the 

EPA-provided values) for the modeling of Unit 4 based upon stack tests, as noted in the "Source" 

column comments in the table. 

3.1 BART Option 1: Dry Sorbent Injection (DSI) for S02 Controls and SNCR 

NOx Controls 

Table 3-2 provides the visibility-affecting Unit 4 emissions for the case with emission controls for S02 

and NOx related to coal firing. Control efficiencies for the various control options were provided by 

TEP. The S02 emission rate of 0.22 lb/MMBtu corresponds to dry sorbent injection (DSI) and 

provides 70% control efficiency, while the NOx emission rate of 0.30 lb/MMBtu corresponds to 

application of Selective Non-Catalytic Reduction (SNCR) and provides 30% control efficiency. All 

BART emission rates refer to a rolling 30-day averaging time. 

3.2 BART Option 2: Dry Scrubber for S02 and H2S04 Controls and SCR NOx 

Controls 

Table 3-2 provides the visibility-affecting Unit 4 emissions for the case with emission controls for S02 

and NOx related to coal firing. The S02 emission rate of 0.080 lb/MMBtu corresponds to dry flue gas 

desulfurization "dry scrubbing" to conserve water resources and maximize removal of sulfuric acid 

mist and provides 89% control efficiency, while the NOx emission rate of 0.050 lb/MMBtu corresponds 

to application of Selective Catalytic Reduction (SCR) and provides 89% control efficiency. 

Both of these BART options would likely involve excess ammonia releases to the atmosphere, 

especially for the SNCR option. The excess ammonia emissions would then combine with gaseous 

S02 and NOx emissions to cause additional haze in both sulfate and nitrate forms that would not be 

present without the NOx controls. Due to the difficulty in simulating this effect in CALPUFF, it is not 

included in the modeling. However, it should be noted that with this omission, the CALPUFF modeling 

results presented below overstate the visibility benefits of the NOx controls. 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM 

Table 3-1 : Unit 4 Exhaust Stack Parameters 

Units 

UTM-X, Zone 12, NAD83 Meters 

UTM-Y, Zone 12, NAD83 Meters 

Stack Height Meters 

Base Elevation Meters 

Effective Diameter Meters 

Gas Exit Velocity m/s 

Stack Gas Exit Temperature deg K 

Unit 4 

Baseline 

508.950 

3558.1 48 

75.59 

794.92 

3.1 3 

36.33 (

1

) 

414.2 

Environment 

Unit 4 Unit 4 

Option 1 Option 2 

(SNCR/051) (SCRIDFGD) 

508.950 508.950 

3558.148 3558.148 

75.59 75.59 

794.92 794.92 

3.13 3.13 

36.33 (1) 32.48 (

2) 

414.2 352.6 

(1 ) The velocity is based on TEP-provided stack measurements. EPA used a lower exit 

velocity of 28.04 m/s. 

(2) The velocity is based on TEP-provided stack measurements, adjusted for temperature 

and increased by 5% to account for added moisture. EPA used a lower exit velocity 

of 21 .67 m/s. 

3-2 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2

013 
AECOM 

Table 3-2: Emissions and Stack Parameters for Sundt Units 1 -43 

Stack Parameters 

Unit/Case Stack Stack Stack Stack Exit S02 

Height Elevation Diameter Temp Velocity 

m m m K m/s g/s 

Unit 1 39.62 794.92 3.21 399.82 8.84 0.222 

Unit 2 39.62 794.92 3.30 399.82 8.23 0.547 

Unit 3 43.89 794.92 3.75 392.04 8.84 0.328 

Unit 4 

(Baseline) 75.59 794.92 3.13 414.2 36.33 117.985 

Unit 4 SNCR 

and DSI 75.59 794.92 3.13 414.2 36.33 35.396 

(Option 1) 

Unit 4 SCR and 

Dry FGD 75.59 794.92 3.13 352.6 32.48 12.978 

(Option 2) 

Environment 

Speciated PMlO 

NOx PMF 

fine PMC EC S04 

g/s g/s g/s g/s g/s 

12.915 0.00

 0.00 0.00

 0.00

 

20.231 0.00

 0.00 0.00

 0.00

 

18.61 0.00

 0.00 0.00

 0.00

 

70.364 0.970 1.007 0.037 2.561 

49.255 0.970 1.007 0.037 2.561 

7. 740 0.768 0.797 0.030 2.897 

SOA 

g/s 

0.00 

0.00 

0.00 

0.642 

0.642 

0.724 

3-3 

Source 

Same as the EPA BART Modeling 

2012 111• 

Same as the EPA BART Modeling 

2012 (ll. 

Same as the EPA BART Modeling 

2012 111• 

EPA BART Modeling 2012 except 

for stack temperature and velocity, 

which are based on TEP full load 

data. 

EPA BART Modeling 2012 except 

for stack temperature and velocity, 

which are based on TEP full load 

data. DSI S02 control effieciency is 

70%. SNCR NOx control effieciency 

is 30%. 

EPA BART Modeling 2012 except 

velocity, which is based on TEP full 

load data adjusted for 

temperature and increased by 5% 

to account for added moisture. 

DFGD S02 control effieciency is 

89%. SCR NOx control effieciency 

is 89%. 

3 Technical Analysis for Arizona and Hawaii Regional Haze FIPs: Task 7: Five-Factor BART Analysis for TEP Sundt (Irvington). EMAQ LOE (EPA Contract EP-D-07-102). 

October 9, 2012. 

Visibility I mprovement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 4-1 

4.0 CALPUFF Modeling Procedures 

In July 2005, EPA issued BART Guidelines that provide guidance to the States in making BART 

determinations for large power plants and other BART-eligible sources

4

. The BART Guideline states 

that modeling may be necessary to support a decision by the States about which BART-eligible 

sources "cause or contribute" to visibility impairment and are subject to BART. 

4.1 CALPUFF Model Formulation for Predicting Visibility Impairment 

EPA guidance recommends CALPUFF for modeling single source visibility impacts at Class I areas. 

The model developer website describes CALPUFF as " ... an advanced non-steady-state 

meteorological and air quality modeling system ... It is maintained by the model developers and 

distributed by TRC. The model has been adopted by the U.S. Environmental Protection Agency (U. S. 

EPA) in its Guideline on Air Quality Models as the preferred model for assessing long range transport 

of pollutants and their impacts on Federal Class I areas and on a case-by-case basis for certain nearfield applications involving complex meteorological conditions. The modeling system consists of three 

main components and a set of pre-processing and post-processing programs. The main components 

of the modeling system are CALMET (a diagnostic 3-dimensional meteorological model), CALPUFF 

(an air quality dispersion model), and CALPOST (a post-processing package)". 

CALPUFF offers three options for dealing with chemical transformations: 

• A pseudo-first-order chemical reaction mechanism for the conversion of S02 to S04 and 

NOx to N03. This mechanism is based on the chemical transformation scheme used in the 

MESOPUFF-115 model and incorporates the most significant dependencies of spatially and 

temporally varying environmental conditions of the transformation rates. 

• The RIVADIARM3 scheme6

, which treats NO and N02 conversion process in addition to 

the N02 to N03 and S02 to S04 conversions, with equilibrium between gaseous HN03 and 

ammonium nitrate aerosol. 

• User-specified 24-hour cycles of transformation rates. 

The Interagency Workgroup on Air Quality Modeling (IWAQM) recommends using the MESOPUFF11 system with CALPUFF. This chemistry option is also the model default recommended by EPA. 

4.2 Ammonia Background Concentrations 

In the CALPUFF model, the oxidation of NOx to nitric acid (HN03) depends on the NOx concentration, 

ambient ozone concentration, and atmospheric stability. Some of the nitric acid is then combined with 

available ammonia in the atmosphere to form ammonium nitrate. The amount of ambient ammonia 

concentrations is a critical input to the CALPUFF model for nitrate formation, especially with the use of 

• US EPA, 2005. BART guidelines, Federal Register update: June 24, 2005. 

5 Scire et. al., 1 984. User's Guide to the MESOPUFF II Model and Related Processor Programs, 1 984. EPA-600 S8-84-013. 

May 1 984. 

• Morris et. al.,1988. Rocky Mountain Acid Deposition Model Assessment: Acid Rain Mountain Mesoscale Model (ARM3), EPA 

1 988. 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 

the MESOPUFF II chemistry. It is important to note that that only particulate nitrate will impact 

visibility, nitric acid would not. 

4-2 

Morris et al.7 reported that the EPA-approved version of CALPUFF with the MESOPUFF II chemistry 

(Version 5.8) was developed from field data limited to ambient temperatures no lower than 50°F. 

Therefore, the use of CAL PUFF for much lower temperatures for the critical winter season represents 

an extension of the model to untested conditions. Morris et al. found that the limitations of the ambient 

temperatures in the field data used in development of the model could result in overestimating sulfate 

and nitrate formation in colder conditions. These investigators found that CALPUFF (version 5.8) 

tended to over-predict nitrate concentrations during winter by a factor of about 3 with high ammonia 

background concentrations. 

Recently, the IMPROVE monitoring network began to incorporate routine measurements of gaseous 

ammonia at specific sites. A recently issued technical paper8 on this subject showed monthly 

ammonia measurements at these sites, including one in southern Arizona (Chiricahua) that was 

modeled for this study. A review of the measurements taken to date at these sites (see Figure 4-1) 

indicates that ammonia concentrations less than below 1 ppb (e.g., 0.5 ppb) are present at this site in 

winter. Note that EPA used a constant value ammonia background level of 1 ppb for all 12 months, 

but without the benefit of the recent IMPROVE measurements. 

In an independent analysis, the Colorado Department of Public Health and Environment (CDPHE) 

performed a sensitivity modeling analysis to explore the effect of the ammonia concentration input to 

CALPUFF on the predicted visibility impacts for a source with high NOx emissions relative to S02 

emissions.9 It is noteworthy that the largest sensitivity occurs for ammonia input values between 1 

and 0.1 ppb. In that range, the difference in the peak visibility impacts predicted by CALPUFF is 

slightly more than a factor of 3 between ammonia concentration input values of 1 and 0.1 ppb. This 

sensitivity analysis shows that the choice of background ammonia is very important in terms of the 

magnitude of visibility impacts predicted by CALPUFF, and that the assumption of 1 ppb for winter 

likely introduces another level of over-predictive conservatism in the modeling results for NOx effects 

upon haze. 

The visibility composition plots depicted in Figure 4-2 are from two IMPROVE monitors located in 

Saguaro West National Park and Saguaro East National Monument show that the majority of nitrates 

(shown by red portions of the composition columns) form during cold temperature (in the modeled 

predictions and in the real world) and, therefore, the model is not sensitive to the selected ammonia 

values in summer, but would be highly sensitive to values in winter months. 

Based upon this newly available ammonia measurement information (which conservatively includes 

both gaseous and particulate form concentration contributions), AECOM has developed a set of 

monthly-varying ammonia background concentrations (see Table 4-1) that correspond to the actual 

measured values noted above. Consistent with the EPA values, an ammonia background of 1 ppb is 

used for many of the non-winter months. 

7 Manis, R., Steven Lau and Bonyoung Koo, 2005. Evaluation of the CALPUFF Chemistry Algorithms. Presented at A&WMA 

9811 Annual Conference and Exhibition, June 21 -25, 2005 Minneapolis, Minnesota. 

8 Chen, X., D. Day, B. Schichtel, W. Maim, J. Mojica, C. McDade, E. Hardison, S. Kreidenweis, and J. Collett, 2012. A Pilot 

Monitoring Study of Atmospheric NHx at Selected IMPROVE Sites. Extended Abstract # 19. Presented at the 2012 Aerosol 

and Atmospheric Optics: Visibility & Air Pollution Specialty Conference, held September 25-28". 2012 in Whitefish. MT. Air & 

Waste Management Association, Pittsburgh, PA. 

9 Supplemental BART Analysis: CALPUFF Protocol for Class I Federal Area Visibility Improvement Modeling Analysis (DRAFT), 

revised June 25, 2010, available at http://ww.colorado.gov/airquality/documents/DraftColoradoSupplementaiBART AnalysisCALPU FFProtocoi-25June201 O.pdf. 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 

Figure 4-1 : 

.-

IMPROVE NHx Concentrations from April 201 1 to January 201 2 

,-

 

5 

0 

·I'll 5tll 6/11 i/11 Sfl l 9'll 1 0111 1 )I ll 1 2d 1 l/11 

-- ROl\IOS 

__,._ WH. 

-r- BONDS 

GL-\CS 

-+- ME\'ES 

C.liR.'I 

-B- B.�S 

_,._ CEBLS 

-&- YELS 

4-3 

Figure 4-2: 2009 IMPROVE Composition Data for Saguaro West National Park ("SAWE1 ") and 

Saguaro East National Park ("SAGU1 ") 

i 

3JO 

10 0 

SAWE1 

.-._j)exl- am

!_bext: CM_bexl· .EC!_bext: 

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� 0 -�--.-�---------·--� 

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Vlsibillty Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 

Table 4-1 : Background Monthly Ammonia Concentrations Used in the Modeling (ppb) 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov 

0.5 0.5 0.6 0.7 1 .0 1 .0 1 .0 1 .0 1 .0 1 .0 1 .0 

4.3 CALMET Modeling Procedures 

44 

Dec 

0.8 

The Western Regional Air Partnership (WRAP) developed six 4-kilometer (km) CALMET 

meteorological databases for three years (2001-2003). The CALMET modeling domains were 

strategically designed to cover all potential BART eligible sources within WRAP states and all 

Prevention of Significant Deterioration (PSD) Class I areas within 300 km of those sources. The 

extents of the six domains are shown in Figure 3-a through Figure 3-1 f of the WRAP common BART 

modeling protocol, available at 

http://pah.cert.ucr.edu/agm/308/bartJWRAP RMC BART Protocol Auq1 5 2006.pdf. The WRAP 

CALMET meteorological inputs, technical options, and processing steps are described in Sections 

2 and 3 of the WRAP protocol. 

U.S. Geological Survey (USGS) 3 arc-second Digital Elevation Model (OEM) files were used by 

WRAP to generate the terrain data at 4-km resolution for input to the six CALMET runs. Likewise, 

the Composite Theme Grid format (CTG) files using Level I USGS land use categories were used 

by WRAP to generate the land use data at 4-km resolution for input to the six CALMET runs. See 

Sections 3.1 .1 .3-3.1.1.4 of the WRAP BART modeling protocol for details on the data processing. 

Three years of 36-km MMS data (2001-2003) were used by WRAP to generate the 4-km subregional meteorological datasets. Section 2 of the WRAP protocol discusses MMS data extraction. 

The BART CALPUFF modeling for Sundt was done using the Arizona 4-km CALMET database with 

application-specific modifications and adjustments later requested by EPA Region 9, such as: 

• AECOM used a smaller R1 value of 18 km and R1 MAX value of 30 km in comparison to the 

R1 of 1 00 km and R1 MAX of 50 km used by WRAP. Shrinking these weighting factors avoids 

abrupt transition of surface winds. The adjusted R1 and R1 MAX values blend the surface 

observations into the MMS observations much better, creating a more uniform wind field 

throughout the domain. 

• When rerunning CALMET, AECOM used the latest EPA-approved version of CALMET 

(Version 5.8, Level 070623) instead of Version 6.21 1 that was used by WRAP. 

4.4 CALPOST Post Processor and Deciview Calculations 

CALPUFF uses predictions of various particulate species to compute the visibility extinction using the 

Interagency Monitoring of Protected Visual Environments (IMPROVE) equation (both original10 and 

1° Federal Land Managers, 2001 . Federal Land Managers' Air Quality Related Values Workgroup (FLAG) Phase I Report. 

http:/fv.N.N/2.nature.nps.govlardlflagfreelindex.htm. 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 4-5 

"new"1 1 versions as documented in the Federal Land Managers' Air Quality Related Values 

Workgroup (FLAG) reports. The update to the IMPROVE equation, adopted in the FLAG 2010 

version, is based upon a re-evaluation of the comparison between particulate species concentrations, 

relative humidity, and directly-observed light scattering. During most of the BART analysis period 

between 2005 and 201 0, however, EPA has relied upon the original IMPROVE equation. 

The model user provides specific inputs for the CAL POST post-processor as noted in FLAG reports 

regarding the use of the original and new IMPROVE equations. In addition to the choice between 

these equations, the CALPOST user needs to define the natural background particulate 

concentrations. The BART Rule specifies that the visibility improvement for various emission cases 

needs to be referenced to "clean" natural conditions, which can be defined in two alternate ways: the 

annual average natural conditions (referred to as option "a") and the conditions associated with the 

20% best days (referred to as option "b"). 

EPA guidance provides each state the option to choose between the two definitions of natural 

conditions. As EPA noted in its July 20, 201 2 proposed rule, Arizona selected the annual average 

natural background and the original IMPROVE equation (also termed "Method 6") for use in the 

State's BART analyses. These selections correspond to "Method 6a" in the terminology adopted in 

EPA's proposed rule. 

The modeling results presented in this document were based on Method 6a, consistent with the 

procedures used by the state of Arizona. 

4.5 CALPUFF Modeling Procedures 

AECOM conducted CALPUFF modeling of the baseline and emission control cases for Sundt using 

the EPA-approved version of CALPUFF (version 5.8).1

2 In recent years, TRC, the company that 

maintains the CALPUFF model, has released a new version (6.42) of CALPUFF to fix certain coding 

"bugs" in EPA-approved version 5.8 and to si�nificantly improve the chemistry module. CALPUFF 

has been evaluated by several investigators 1 ·14'15 and the results indicated that the EPA-approved 

version using the MESOPUFF II chemistry significantly over-predicts nitrate formation in wintertime 

conditions. However, EPA has been slow to adopt this version of CALPUFF or even fix the bugs in 

version 5.8, so we are currently left with that version for BART modeling. As a result, the predicted 

visibility improvements for NOx controls are overstated as a result of the known biases of the 

chemistry algorithm used in CALPUFF v. 5.8. 

11 Federal Land Managers, 201 0. Federal Land Managers' Air Quality Related Values Work Group (FLAG) Phase I ReportRevised (2010). Natural Resource Report NPS/NRPC/NRR-2010/232. 

http//nature.nps.gov air/pubs/pdf/fla /FLAG 201 0. pdf. 

'2 AECOM used the EPA-approved version of CALPUFF (Version 5.8, Level 070623) that has been posted at 

http://w.vw.src.com/calpuff/download/download.htm#EPA VERSION. 

13 Scire, J.S., Z-X Wu, D.G. Strimaitis and G.E. Moore, 2001: The Southwest Wyoming Regional CALPUFF Air Quality Modeling 

Study - Volume I. Prepared for the Wyoming Dept of Environmental Quality. 

1• Karamchandani, P., S. Chen, R. Bronson, and D. Blewitt, 2009. Development of an Improved Chemistry Version of 

CALPUFF and Evaluation Using the 1 995 S#INYT AF Data Base. Presented at the Air & Waste Management Association 

Specialty Conference on Guideline on Air Quality Models: Next Generation of Models. October 28-30, 2009, Raleigh, NC. 

15 Monis, R., Steven Lau and Bonyoung Koo. 2005. Evaluation of the CALPUFF Chemistry Algorithms. Presented at A&WMA 

9811 Annual Conference and Exhibition, June 21-25, 2005 Minneapolis, Minnesota. 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 4-6 

The BART Rule indicates that a source will screen out of a BART determination if the baseline 

emissions show visibility impairment relative to natural conditions below 0.5 delta-deciview (the 

"contribution" level), if the state selects this level for the screening threshold. Arizona has selected a 

0.5 delta-deciview threshold for this purpose. 

The CALPUFF computational modeling domain was defined based on a 50-km buffer around each of 

the ten Class I area, shown in Figure 2-2. A 50-km buffer around each Class I area accounts for puff 

re-circulations. Using a smaller computational grid within the WRAP CALMET domain minimizes 

computation time and output file size. 

The receptors used for each of the Class I areas are based on the National Park Service database of 

Class I receptors. 

WRAP has developed hourly ozone measurement files for three years (2001-2003), available at 

http://pah.cert.ucr.edu/aqm/308/bart/calpuff/ozone daU. Data collection and processing are described 

in Section 3.1 .2.7 of the WRAP protocol. These ozone data files were used as input to CALPUFF. 

AECOM ran each emission scenario with the monthly-variable ammonia background concentration, 

as shown in Table 4-1 . 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 

5.0 Visibility Improvement Modeling Results 

5.1 Baseline Emissions Modeling Results for BART Screening 

5-1 

The first step in the BART review was the modeling of baseline emissions to determine whether any 

Class I areas are associated with visibility impairment relative to natural conditions exceeding 0.5 

delta-deciview (delta-dv). Results presented in Table 5-1 are the 3-year average of the 98th percentile 

delta-dv predicted impacts for each Class I area. 

The BART guidelines indicate that sources are exempt from BART determinations if they do not cause 

or contribute to visibility impairment at Class I areas. Except for Saguaro National Park, this is the 

case for the baseline emissions from the Sundt Generating Station; the 98th percentile day's impacts 

are less than 0.5 delta-dv. Therefore, the focus of the visibility improvement analysis is on Saguaro 

National Park. Due to the fact that the haze impacts are higher for the eastern portion of this Class I 

area, the BART determination modeling focused upon that area. 

For supplemental information, the visibility improvement for the candidate BART control options that 

we modeled at other parks for which Sundt does not contribute to visibility impairment is provided in 

Appendix A. 

Table 5-1 : 981h Percentile Baseline Case CALPUFF Modeling Results* for Visibility Impairment, deltadeciview 

Class I Area Baseline 

Mazatzal W 0.04 

Gila W 0.08 

Mt. Baldy 0.05 

Sierra Ancha 0.06 

Galiuro W 0.45 

Superstition W 0.12 

Pine Mountain W 0.03 

Chiricahua W 0.1 8 

Chiricahua NM 0.1 9 

Saguaro East NP 1 .37 

Saguaro West NP 1 .01 

* 96., percentile day's visibility impairment over 3 years modeled, relative to natural conditions 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 5-2 

5.2 BART Control Option Visibility Modeling Results 

The results of the BART control options visibility modeling for Saguaro National Park (eastern portion) 

are presented in Table 5-2. This table shows the improvements in the visibility impairment for the two 

control options relative to the baseline case for Saguaro National Park. It is noteworthy that as the 

plume temperature is lowered by the S02 controls, especially associated with dry FGD, the terrain 

impacts at Saguaro National Park result in visibility degradation for Option 2 relative to Option 1. 

The next sub-section discusses the effectiveness of these control options. 

Table 5-2: Visibility Improvement* over Baseline Conditions, delta-deciview 

Visibility Visibility 

Improvement for Improvement for 

Class I Area Option 1: Option 2: 

SNCRJDSI SCRIDFGD 

on Unit 4 on Unit 4 

Saguaro East NP 0.1 64 0.1 28 

• 98th percentile day's visibility impairment over 3 years modeled 

5.3 Visibility Improvement Effectiveness Metrics 

Although the BART Rule implies, but does not specifically provide, metrics for determining whether 

BART control options have sufficient visibility improvement for a reasonable cost to be recommended, 

actual policies developed in practice over the years since the BART Rule was issued can be drawn 

upon to provide guidance in this respect. There are two types of metrics available: 

• The magnitude of the visibility improvement, expressed in deciviews averaged over the years 

modeled, should be higher than a minimal value that is related to the ability for measurement 

systems to actually detect a difference between measurements of visibility that could be 

identical . There are also policy-related statements of minimal visibility improvement 

magnitudes. 

• The cost effectiveness of the visibility improvement, expressed in dollars per deciview, should 

be higher than a benchmark value established by the Federal Land Managers. 

These metrics are further discussed below. 

5.3.1 Magnitude of Minimum Visibility Improvement 

• The northeastern states Regional Planning Organization, MANE-VU (as documented by 

many states; see www mass.gov/de /airpriorities/hazebart doc , has determined that a 

"degree of visibility improvement" that is very small (<0.1 delta-deciview) is such that no 

reasonable weighting could justify additional controls under BART. 

• EPA's Regional Haze Rule mentions 16 that "no degradation" to visibility would be 

"defined as less than a 0.1 deciview increase." 

16 64 FR 35730. 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 5-3 

• For the Reid Gardner Generating Station BART visibility analysis 17

, EPA selected SNCR 

over SCR controls because the incremental visibility improvement between the two 

options was only 0.1 delta-dv; too small to justify the cost of installing SCR. 

• The uncertainty in measurements of identical visibility conditions reported by Tombach 

(2002)16 is estimated to be about 0.3 delta-deciview. 

• In its consideration of a proposed secondary PM2.5 NAAQS involving visibility, EPA 

documented19 measurement uncertainties in the visibility index (VI) indicate a t�pical 

uncertainty in the VI of 2%. With current (baseline) measurements of visibilitl for the 

20% worst days at Saguaro National Park at about 1 5.5 deciviews, this uncertainty is on 

the order of 0.3 delta-deciview. 

Based upon this information, it is reasonable to conclude that a predicted visibility improvement on the 

order of 0.1 delta-deciview or less can clearly be dismissed as insignificant. Furthermore, it is evident 

that a visibility improvement less than 0.3 delta-deciview cannot be detected with current 

measurement systems. That value is also below the 0.5 delta-deciview level of "contribution" to haze 

in the BART rule, and is only 30% of the 1 delta-deciview value that the BART Rule mentioned as 

being visually discernible by the human eye ("causing haze"). Therefore, a visibility improvement less 

than 0.3 delta-deciview should be considered as being too small to distinguish from no change in 

visibility whatsoever (and is well below the "contribution" and "cause" thresholds in the BART Rule), so 

it can also be considered as insignificant for consideration as BART control option to be adopted. 

5.3.2 Visibility Improvement Cost Effectiveness 

As noted above, EPA BART regulations do not establish specific thresholds for cost-effectiveness. 

However, the Federal Land Managers (FLMs), in numerous correspondences21 to states, have 

referred to a benchmark of $20 million per deciview as a threshold for excessively high costs for the 

degree of visibility improvements. This metric is computed by dividing the annualized cost of the 

control (relative to a reference case such as baseline conditions or another BART option) divided by 

the 981h percentile day's visibility improvement relative to the reference case, averaged over the years 

modeled. 

17 EPA Federal Register I Vol. 77, No. 164 f Thursday, August 23, 2012/ Rules and Regulations, page 50938. 

18 Tombach, 1., 2002. Implication of Aerosol Measurement Uncertainty on Tracking of Progress in Mitigating Regional Haze. 

Paper # 42617. Presented at the 95th Annual Conference and Exhibition of the Air & Waste Management Association. 

Baltimore, MD. Available at http://IMv

.atmospheric-research.com/PDFsNisibilitvTracking.pdf. 

19 Papp, M., 2012. Documentation of Measurement Uncertainty Estimates of Collocated Chemical Speciation Network and 

IMPROVE Data for Use in the Secondary PM2 s Standard for Visibility. Available at 

http/ fwv.tv

. epa. gov/ttnnaags/s tandards/pm/data/20 1 20613Pap pdf. 

20 ht

Page 40 of the Arizona Regional Haze Rule State Implementation Plan, available at 

v/environ/airlhaze/downloadlhaze308sip.pdf. 

21 ht

See http:/fwv.tv

.nature.nps.gov/air/regs/sipletPennsylvania 08-02-2010.pdf, 

nature.nps.gov/air/regs/sipet EPA Letter 08-17 -201 1 .pdf, and 

http:/fwv.

.dec.state.ak.us/AIR!ap/docGVEA%20BART%20NPS%20Comments%206-15-09.odf. 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 201

3 
AECOM Environment 

5.3.3 Visibility Modeling Results 

The results presented in this section indicate that both candidate controls result in visibility 

improvements well below 0.3 delta-deciview at the Saguaro National Park. Therefore, the visibility 

improvements are too low to be considered as BART just due to their very small magnitudes, which 

are themselves overstated due to ammonia slip which was not considered in the conservative 

CALPUFF version 5.8 modeling. 

5-4 

The largest visibility benefits at the Saguaro National Park for the DSI/SNCR and DFGD/SCR controls 

are 0.162 and 0.128 delta-dv, respectively. TEP has provided annualized cost information for these 

two control options as follows: 

• DSI + SNCR: $ 6,1 59,954 

• DFGD + SCR: $ 27,1 30,657 

The resulting visibility cost-effectiveness metrics are, therefore, about $38,000,000/dv for DSI/SNCR 

and about $21 2,000,000 for DFGD/SCR. These visibility cost-effectiveness values are well above 

the benchmark value of $20,000,000/dv, especially Option 2 (DFGD/SCR). 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 6-1 

6.0 Conclusions 

The United States Environmental Protection Agency (EPA) Region 9 is anticipated to focus in the near 

future upon a Best Available Retrofit Technology (BART) evaluation for the Sundt Unit 4, which can be 

fired with either coal or natural gas and is located in Tucson, Arizona. Tucson Electric Power (TEP) 

does not believe Sundt Unit 4 is BART eligible, however, TEP has asked AECOM to provide a 

comparative visibility assessment for two emission control options for this coal-fired unit: 

• Option 1: S02 control using dry sorbent injection (providing 70% control over the baseline 

emission rate), and NOx control using Selective Non-Catalytic Reduction (providing 30% 

control over the baseline emission rate). 

• Option 2: S02 control using dry flue gas desulfurization ("dry scrubbing", providing 89% 

control efficiency), and NOx control using Selective Catalytic Reduction (providing 89% 

control efficiency). 

AECOM has conducted new modeling with the following changes from EPA's modeling: 

• Updated exit velocity for Unit 4 was modeled based on revised stack measurements provided 

by TEP. The exit velocity TEP provided was about 34% higher than EPA used. 

• TEP estimated a revised (70%) control efficiency for the dry sorbent injection (OS I) S02 

emission controls, slightly lower than what EPA used (75%). 

• Based upon newly available ammonia measurement information, AECOM used as input to 

CALPUFF a set of monthly-varying ammonia background concentrations that correspond to 

the actual measured values during winter at a Class I area being modeled in southern 

Arizona, which range from 0.5 to 1 .0 ppb. EPA had applied a 1 .0 ppb ammonia value for all 

months of the year. 

The visibility improvement modeling review was conducted for all Prevention of Significant 

Deterioration Class I areas within 300 km of the plant, using the CALPUFF model version 5.8. This 

model has a known over-prediction bias for nitrate haze formation that overstates the visibility 

improvements for the candidate BART options. The modeling also does not account for the hazecausing effects of ammonia slip from the NOx emission controls that were evaluated. 

Even with these over-prediction biases, the results of the analysis indicate that the only Class I area 

with 98th percentile daily impacts above the BART screening level of 0.5 delta-deciview is Saguaro 

National Park. At this park, the candidate controls result in levels of visibility improvement that are too 

low to be detected (or distinguished from no change in haze) by the available technology for 

particulate monitors (well below the detection threshold of 0.3 delta-deciview) and are less than 20% 

of the perceptible levels that can be visually detected (1 deciview). Furthermore, the cost 

effectiveness of both control options is higher than the Federal Land Manager-established benchmark 

of $20 million/dv. Accordingly, we conclude that neither of these control options would provide cost 

effective visibility improvement and therefore based on the EPA's criteria, it is not reasonable to 

require additional controls of S02 or NOx at Sundt Unit 4. 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 

Appendix A 

Visibility Model ing Results 

for All C lass I Areas 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unit 4 May 2013 
AECOM Environment 

Table A-1 98th Percentile CALPUFF Modeling Results* for Visibility Impairment, delta-deciview 

Option 1 Option 2 

Class I Area Baseline Unit 4 Unit 4 

SNCRIDSI SCRIDFGD 

Mazatzai W 0.04 0.02 0.02 

Gila W 0.08 0.04 0.03 

Mt. Baldy 0.05 0.03 0.02 

Galiuro W 0.45 0.33 0.25 

Sierra Ancha 0.06 0.03 0.02 

Superstition W 0.12 0.06 0.04 

Pine Mountain W 0.03 0.02 0.01 

Chiricahua W 0.18 0.11 0.08 

Chiricahua NM 0.1 9 0.12 0.08 

Saguaro East NP 1 .37 1 .21 1 .24 

Saguaro West NP 1 .01 0.86 0.85 

• '" ' . . .. . . 98 percentile day s VISibility 1mpa1rment over 3 years modeled, relative to natural cond1t1ons 

Table A-2: Visibility Improvement* over Baseline Conditions, delta-deciview 

• 

Visibility Visibility 

Improvement for Improvement for 

Class I Area Option 1: Option 2: 

SNCRIDSI SCRJDFGD 

on Unit 4 on Unit 4 

Mazatzai W 0.019 0.028 

Gila W 0.038 0.054 

Mt. Baldy 0.020 0.029 

Galiuro W 0.1 25 0.203 

Sierra Ancha 0.028 0.038 

Superstition W 0.054 0.073 

Pine Mountain W 0.013 0.019 

Chiricahua W 0.063 0.1 00 

Chiricahua NM 0.069 0.1 12 

Saguaro East NP 0.1 64 0.128 

Saguaro West NP 0.1 47 0.1 62 

m I 0 • • • 98 percentile day s VISibility 1mpa1rment over 3 years modeled 

Visibility Improvement Analysis for Candidate BART Control Options: Sundt Unft 4 May 2013 
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